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Secondary transmission of H1N1 in households low

Two recent medical studies have concluded that secondary transmission of H1N1 virus in households is low. Both reports were published recently on the online edition of Epidemiology and Infection.

Cidrap.umn.edu reports that this may confirm suspicions that the virus may be less contagious than pandemic viruses and some seasonal flu viruses of the past.

The first study looked at household transmission rates in boys with pandemic flu at a camp in Florida last summer. Researchers in this case confirmed that 49 out of 212 boys at the camp had probable or confirmed cases of H1N1, cidrap.umn.edu reports. This placed the attack rate at 23 percent. Out of 87 household contacts, however, the researchers found only three cases of secondary transmission for an attack rate of only 3.5 percent.

The second study examined the households of Hong Kong secondary school students sickened during an outbreak in June 2009.

Researchers in this study said 65 of 511 students got sick during the outbreak. A total of 12 confirmed H1N1 infections were found among 205 of the sick students' household contacts, placing the secondary attack rate of 5.9 percent, cidrap.umn.edu reports.

Additionally, the Hong Kong researchers concluded household contacts younger than 18 were 15 times more likely to be infected than older contacts.

These secondary infection rates found in the two studies were even lower than those found in an earlier study published in the December 2009 edition of the New England Journal of Medicine, according to the cidrap.umn.edu report.